Solid state energy storage devices

ABSTRACT

Described in this patent application are devices for energy storage and methods of making and using such devices. In various embodiments, blocking layers are provided between dielectric material and the electrodes of an energy storage device. The block layers are characterized by higher dielectric constant than the dielectric material. There are other embodiments as well.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/749,706,filed Jan. 25, 2013, entitled “SOLID STATE ENERGY STORAGE DEVICES,”which claims priority to Application No. 61/592,517, filed Jan. 30,2012, the contents of which are hereby incorporated in their entirety byreference for all purposes.

BACKGROUND OF THE INVENTION

Described in this patent application are devices for energy storage andmethods of making and using such devices.

In general, a capacitive energy storage device comprises two electrodeswith a dielectric material disposed between the electrodes. FIG. 1 is asimplified diagram illustrating a capacitive energy storage device. Asshown in FIG. 1, dielectric material 103 is positioned between theelectrodes 101 and 102. Upon application of a voltage across theelectrodes the dielectric material becomes polarized and charges arestored on the electrode plates.

Unfortunately, conventional energy storage devices are inadequate, asexplained below. It is desirable to have new and improved energy storagedevices.

BRIEF SUMMARY OF THE INVENTION

Described in this patent application are devices for energy storage andmethods of making and using such devices. In various embodiments,blocking layers are provided between dielectric material and theelectrodes of an energy storage device. The block layers arecharacterized by higher dielectric constant than the dielectricmaterial. There are other embodiments as well.

In an embodiment, the present invention provides an energy storagedevice that includes first and second electrodes that are spaced apart.A dielectric layer is disposed between the first and second electrodes.A first blocking layer is disposed between the first electrode and thedielectric layer and a second blocking layer is disposed between thesecond electrode and the dielectric layer. The dielectric constants ofthe first and second blocking layers are both independently greater thanthe dielectric constant of the dielectric layer.

Depending on the application, the dielectric material may differentrelative permittivity, which can be between about 2 and 25, betweenabout 3 and 15, or other range. The dielectric layer can have a materialcharacterized by a band gap of greater than 4 eV. The dielectric layercan also have a material characterized by a breakdown field strength ofgreater than 0.5V/nm.

The dielectric layer may comprise a material selected from oxides,nitrides, oxynitrides and fluorides. The dielectric layer may alsocomprise a material selected from SiO₂, Al₂O₃ or Si₃N₄.

The blocking layers, with higher relative dielectric constant, can havea relative permittivity of greater than 20. The material of the blocklayers can have a band gap of less than 4 eV, and the breakdown fieldstrength can be between 1 mV/nm and 200 mV/nm. Depending on theapplication, the first and second blocking layers may independentlycomprise a material selected from ionically conducting materials andnon-ionically conducting materials. Depending on the application, theionically conducting material can be selected from Li⁺, H⁺, Mg²⁺, Na⁺,O⁻, F⁻ conductors, Li₃PO₄, and Li₃PO_(4-x)N_(x). The non-ionicallyconducting materials can be multiferroic high k materials, such asCaCu₃Ti₄O₁₂, La₂ nanocomposite high-k materials, high-k ceramicmaterials, ferroelectric perovskites materials, PZT(Pb(Zr_(0.5)Ti_(0.5))O₃), SrTiO₃, PbTiO₃, BaTiO₃, (BaSr)TiO₃, or others.

The first and second blocking layers independently comprises a materialhaving a dielectric constant between 10 and 10000 times the dielectricconstant of the material comprising the dielectric layer. In a specificembodiment, the first and second blocking layers independently comprisea material having a dielectric constant between 50 and 1000 times thedielectric constant of the material comprising the dielectric layer. Thefirst and second blocking layers independently may have a thickness ofbetween 4 nm and 100 nm. In a specific embodiment, the dielectric layerhas a thickness of between 10 nm and 10 um. The first and secondblocking layers independently may have a thickness of between 10 and1000 times the thickness of the dielectric layer.

It is to be appreciated that the block layer and dielectric layermaterial vary depending on the application. In an embodiment, the firstand second blocking layers are both PZT and the dielectric layer isSiO₂. In another embodiment, the first and second blocking layers areboth LiPON and the dielectric layer is SiO₂. In another embodiment, thefirst and second blocking layers are both LiPON and the dielectric layeris Li₂O. In yet another embodiment, the first and second blocking layersare both LiPON and the dielectric layer is LiF.

The blocking layers can also have different material. In an embodiment,the first blocking layer comprises a cation conducting material and thesecond blocking layer comprises an anion conducting material. In anotherembodiment, the first blocking layer comprise an anion conductingmaterial and a cation conducting material. In yet another embodiment,the second blocking layer comprise an anion conducting material and acation conducting material.

With the structure described above, the device can have an energydensity of between 5 and 1000 Whr/kg, an energy density of between 10and 650 Whr/kg, or an energy density of between 50 and 500 Whr/kg. Incertain embodiment, an energy density can greater than 50 Whr/kg, orgreater than 100 Whr/kg.

The first electrode can have a work function greater than the workfunction of the second electrode. The work function of the firstelectrode can be greater than 4.0 eV and the work function of the secondelectrode can be less than 4.5 eV.

It is to be appreciated that embodiments of the present inventionprovides various advantages over conventional techniques. In this patentapplication, energy storage devices are capable of sustaining higherfield strengths than conventional capacitive energy storage devices andwhich may therefore be used for high energy density capacitive energystorage. More specifically, energy storage devices according to thepresent invention are capable of withholding higher breakdown voltages(and therefore improved stability and reliability) compared toconventional devices, a thereby allowing a higher level of energydensity. There are other benefits as well as described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating a capacitive energy storagedevice.

FIG. 2 shows exemplary current voltage curves for a capacitive energystorage device.

FIG. 3 shows the permittivity and breakdown field strength of a numberof common dielectrics.

FIG. 4 shows one version of a high energy density energy storage device.

FIG. 5 illustrates energy density due to onset of Fowler-Nordheimtunneling.

FIG. 6 shows a calculation of the density of states (DOS) of Li₃PO₄ andLi₃PO_(4-x)N_(x) that shows that these materials.

FIG. 7 shows one version of the devices that includes electrodes and andmultiple layers of dielectric material separated by layers of blockingmaterial.

FIG. 8 illustrates a device 800 that includes first and secondelectrodes, a dielectric layer disposed between them, and first andsecond blocking layers.

FIG. 9 illustrates breakdown voltage of energy storage devices.

FIG. 10 is a graph illustrating performance of an exemplary energystorage device with SiO₂ as dielectric material and PZT as blockingmaterial according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Described in this patent application are devices for energy storage andmethods of making and using such devices. In various embodiments,blocking layers are provided between dielectric material and theelectrodes of an energy storage device. The block layers arecharacterized by higher dielectric constant than the dielectricmaterial. There are other embodiments as well.

Capacitive energy storage has well-known advantages versuselectrochemical energy storage, e.g. in a battery. Compared tobatteries, capacitors are able to store energy with very high powerdensity, i.e. charge/recharge rates, have long shelf life with littledegradation, and can be charged and discharged (cycled) hundreds ofthousands or millions of times. However, capacitors often do not storeenergy in as little volume or weight as in a battery, or at low cost perenergy stored, making capacitors impractical for applications such as inelectric vehicles. Accordingly, it would be an advance in energy storagetechnology to provide a capacitive energy storage capable of storingenergy more densely per volume and/or mass.

FIG. 2 shows exemplary current voltage curves for a capacitive energystorage device. Generally the voltage across the electrodes, V, will besome function of the charge stored on the electrodes, Q, as shown in thesolid line curve in FIG. 2. There will be some maximum voltage, V_(max),up to which the device can be charged before the dielectric materialstarts to breakdown. For linear materials the capacitance does notdepend on Q and V(Q)=Q/C as shown in the dotted line B in FIG. 2.

The total energy stored in the device is generally given by:

Total Energy=∫_(v) ^(Qmax) V(A)dQ  (1)

which for linear materials reduces to:

Total Energy=½C*V _(max) ²  (2)

The capacitance, C, is equal to the area of electrodes, A, times thepermittivity, ∈, of the dielectric material divided by the distancebetween the electrodes, d. The energy density of the device, ρ, cantherefore be written as

ρ=½∈*E _(max) ²  (3)

where E_(max) is the maximum sustainable field in the dielectricmaterial and is equal to V_(max)/d.

As can be seen in equation 3, the energy density of a device may beincreased by increasing the permittivity of the dielectric materialand/or by increasing the maximum field sustainable in the dielectricmaterial. Capacitive energy storage has been limited by the relativelylow field strengths sustainable in conventional high permittivitydielectric materials as shown in FIG. 3, which shows the permittivityand breakdown field strength of a number of common dielectrics. Thedotted line on FIG. 3 indicates that the energy density of standarddielectric materials is limited to about 3 Wh/L.

In this patent application are described energy storage devices capableof sustaining higher field strengths than conventional capacitive energystorage devices and which may therefore be used for high energy densitycapacitive energy storage.

FIG. 4 shows one version of a high energy density energy storage devicedescribed herein. The device (400) includes first and second electrodes(410 & 420) spaced apart and a dielectric layer (430) disposed betweenthe electrodes. The device also includes blocking layer (440) disposedbetween the first electrode and the dielectric layer and blocking layer(450) disposed between the second electrode and the dielectric layer.The blocking layers, 440 and 450, are made of materials with higherdielectric constant than that of the material of the dielectric layer.The blocking layers, 440 and 450, may be the same material or may bedifferent materials.

In this patent application the dielectric layer is also referred to asthe “low-k material” and the blocking layers is also referred to as the“high-k material.” The designations “high” and “low” indicate therelative magnitudes of the dielectric constants of the materials nottheir absolute values.

Without being bound by theory, it is believed that the structure shownin FIG. 4 has increased breakdown tolerance, and hence higher energydensity, because of the suppression by the blocking layers of injectionof charge carriers from the electrodes into the dielectric material. Asshown in FIG. 5, it is believed that this device may have high energydensity because the onset of Fowler-Nordheim (FN) tunneling from theelectrodes into the dielectric material is delayed to higher voltages.The delay of FN tunneling results from the scarcity of charge carriersat the low-k material interface. FIG. 5 shows that the area B is largerthan area A. Tunneling probability of an electron at the interface isinversely related exponentially to the area under the potential barrier(from the WKB approximation). So by increasing the barrier height, thearea B will be larger, and the probability of detrimental electrontunneling is exponentially lower. Further, if a double layer is presentat the interface, if the double layer has a charge that repels electronsFN tunneling will be further suppressed. For example, if the leftmosthigh-k layer in the example above has anion conduction, the anions willcreate a double layer at the high-k/low-k interface, and this negativecharge will repel electrons from this interface.

The dielectric layer may generally be made of any dielectric material.In one version of the devices the dielectric layer material has abreakdown field strength of greater than 0.5 V/nm. Breakdown fieldstrength is determined by (i) placing a layer of about 50 nm thicknessof the test material between conductive electrodes one of which isapproximately circular with a diameter of 100 μm and the other of whichis larger than the 100 μm electrode; (ii) applying a linear voltage rampacross the electrodes, ramping up from 0V at a rate of about 0.1V/s;and, (iii) measuring the current flowing between the electrodes as afunction of applied voltage. The breakdown voltage is measured atapproximately room temperature. A typical current-voltage plot ispresented in FIG. 9, showing an initial low voltage region (910) and abreakdown region (920). The breakdown voltage is calculated as thevoltage at which the current is ten times the measured capacitivecharging current. In FIG. 9, for example, if the capacitive chargingcurrent is 10⁻¹⁰ A the breakdown voltage is about 1V (940) at which thecurrent is 10⁻⁹ A. The breakdown field strength is calculated as thebreakdown voltage divided by the thickness of the test material, whichmay be measured by cross-sectional TEM, X-ray reflectometry (XRR) orellipsometry. The current fluctuations shown at about 0.8 V (930) aretypical of such current-voltage plots and are seen at voltagesapproaching the breakdown voltage.

In another version of the devices the dielectric layer material has arelative permittivity of less than 15. The relative permittivity ismeasured by placing a layer of test material of thickness d between twoconductive electrodes of area A and scanning the voltage at scan rate s,measuring the capacitive charging current I, and calculating therelative permittivity, ∈, as the ratio ∈=(I/s)*(d/∈₀A). The relativepermittivity is measured at approximately room temperature.

In another version of the devices the dielectric layer material has aband gap of greater than 4 eV. The breakdown field strength, relativepermittivity and band gap described in this parapgraph are materialproperties of the material that may be used for the dielectric layer;they are not the material properties of the composite blockinglayer/dielectric layer/blocking layer system.

Specific dielectric layer materials that may be used include SiO₂, HfO₂,Al₂O₃, Si₃N₄, oxides, nitrides, oxynitrides and fluorides. In oneversion the dielectric layer material is SiO₂, HfO₂, Al₂O₃ or Si₃N₄.

The blocking layer may generally be made of any material having adielectric constant greater than that of the dielectric constant of thedielectric layer material. In one version of the devices the blockinglayer material has a breakdown field strength of between 1 mV/nm and 200mV/nm. In another version of the devices the blocking layer material hasa relative permittivity of greater than 100. In another version of thedevices the blocking layer material has a band gap of less than 4 eV. Inone version of the device, the blocking layer material is ionicallyconducting, has an relative permittivity of greater than 100 and a bandgap of greater than 3 eV. The breakdown field strength, relativepermittivity and band gap described in this paragraph are materialproperties of the material that may be used for the blocking layer; theyare not the material properties of the composite blockinglayer/dielectric layer/blocking layer system.

The blocking layer material may be an ionically conducting material or anon-ionically conducting material.

In the case of an ionically conducting blocking layer material, thematerial derives its permittivity at least in part from ion migrationwithin the material, establishing double layers at each interface. Thesedouble layers may be engineered to further deplete the electronconcentration at the interface to delay the onset of FN tunneling, as isdescribed in FIG. 5. In one version the ionically conducting material isan anion conductor. In one version the ionically conducting material isa cation conductor. In one version the ionically conducting material isa Li⁺, H⁺, Na⁺, O²⁻ or F⁻ conductor. In one version the ionicallyconducting material is a L⁺ ion conductor. In one version the ionicallyconducting material Li₃PO₄ or Li₃PO_(4-x)N_(x). As used in this patentapplication, LiPON means Li₃PO_(4-x)N_(x). FIG. 6 shows a calculation ofthe density of states (DOS) of Li₃PO₄ and Li₃PO_(4-x)N_(x) that showsthat these materials, along with having a high relative permittivity,have a high bandgap, further delaying the onset of FN tunneling. In oneversion of the devices, the first blocking layer is an anion conductingmaterial and the second blocking layer is a cation conducting material.

In one version of the devices, one or both of the blocking layerscomprises an anion conducting material and a cation conducting material.An example of such device is shown in FIG. 8 in which a device (800)includes first and second electrodes (810 & 820), a dielectric layer(830) disposed between them and first and second blocking layers (840 &850) disposed between the dielectric layer and the first and secondelectrodes respectively. The first and second blocking layers includeanion conducting material (860 & 880) and cation conducting material(870 & 890). In other versions, only one of the first or second blockinglayers includes both cation and anion conducting materials and the otherblocking layer includes either a non-ionically conducting material or acation or anion conducting material. In some version of the devices,independently for the first and second blocking layers the anionconducting material is proximate to the electrode and in other versionsof the devices the cation conducting material is proximate to theelectrode.

In the case of a non-ionically conducting blocking layer material, thematerial derives its permittivity at least in part from the intrinsicpolarizability of the material. In one version the non-ionicallyconducting material is a high-k ceramic material. In one version thenon-ionically conducting material is a ferroelectric perovskite. Inanother version the non-ionically conducting material is PZT(Pb(Zr_(0.5)Ti_(0.5))O₃). In another version the non-ionicallyconducting material is SrTiO₃, PbTiO₃, BaTiO₃ or (BaSr)TiO₃. In anotherversion the non-ionically conducting material is a multiferroic high kmaterial. In another version the non-ionically conducting material isCaCu₃Ti₄O₁₂ or La_(2-x)Sr_(x)NiO₄. In another version the non-ionicallyconducting material is a nanocomposite high-k material.

As described above, the blocking layer material has a higher dielectricconstant than that of the dielectric layer material. In one version ofthe devices, the dielectric constant of the blocking layer material isbetween 10 and 10000 times greater than the dielectric constant of thedielectric layer material. In another version the dielectric constant ofthe blocking layer material is between 100 and 1000 times greater thanthe dielectric constant of the dielectric layer material.

The electrodes may generally be made of any conducting material that iscompatible with the materials of the device with which they havecontact. In one version the electrodes may, independently, be made ofPt, Cu, Al, Ag or Au. The electrodes may be of the same or differentmaterials. In one version, the electrodes have different work functions.In one version the electrode that is positively biased during charge hasa work function that is lower than that of the work function of theelectrode that is negatively biased during charge. In one version theelectrode that is positively biased during charge has a work function ofless than 4.5 eV. In one version the electrode that is negatively biasedduring charge has a work function of greater than 4.0 eV.

The blocking layer may generally be of any thickness that maintains thecharge carrier injection suppression function of the layer. In oneversion the blocking layer has a thickness of between 4 nm and 100 nm.The dielectric layer may generally be of any thickness that maximizesenergy storage density while maintaining an insulating property underhigh field. In one version the dielectric layer has a thickness ofbetween 20 nm and 10 μm. As shown in the calculation below it may beadvantageous for the dielectric layer to be thicker than the blockinglayers. In one version the dielectric layer is between 1 and 1000 timesthe thickness of the blocking layer.

Calculations have shown that the energy is primarily stored in thematerial of low-k, as illustrated by the following example:

Exemplary Properties of High k and Low k Materials:

Low k High k material material Material permittivity 800 4 BreakdownField V/nm 0.1 20 Max absolute V 20000 — voltage Material density g/cm³5 2.65

Calculated Energy Density:

Thickness Voltage drop Field Energy Energy [nm] [V] [V/nm] [Wh/L][Wh/kg] High k layer 1 50 5.0 0.10 9.8 Low k layer 1.00E+03 19990.019.99 1964.7 High k layer 2 50 5.0 0.10 9.8 Total 1100 20000 1787.0624.0

The above example illustrates that energy densities exceeding those instate-of-the-art batteries may be achieved with such devices.

Multiple Layer Devices:

FIG. 7 shows one version of the devices, device 700, that includeselectrodes 710 and 720 and multiple layers of dielectric material (730,740, 750) separated by layers of blocking material (760, 770, 780, 790).

Laminate Devices:

In one version of the devices, the dielectric and blocking layers arelaminate layers in direct contact with each other with the architecturesshown in FIGS. 4, 7 and 8 and as otherwise described herein. In otherversions the devices include one or more interfacial layers between oneor more of the electrodes, dielectric layer and blocking layers.

Energy Density:

In one version a device as described herein has an energy density ofbetween 5 and 1000 Whr/kg. In another version a device as describedherein has an energy density of between 10 and 650 Whr/kg. In anotherversion a device as described herein has an energy density of between 50and 500 Whr/kg. In another version a device as described herein has anenergy density of greater than 50 Whr/kg. As used herein, energy densityif the energy density at the device level; i.e., the total energy storedin the device divided by the mass of the device.

Making of the Devices:

The devices described herein may be fabricated in a number of ways, forexample using sputtering, PVD, ALD or CVD. In one method of makingdescribed herein, the devices are fabricated by sputtering using anEndura 5500, 200 mm by Applied Materials. In one version of the devices,laminate devices are fabricated by sequential deposition of the blockinglayers, dielectric layer(s) and electrodes on a substrate. In oneversion, a substrate is not required and the blocking layers, dielectriclayer(s) and electrode layer(s) may be deposited directly on to one ofthe electrodes.

Uses of the Devices:

The devices described herein may generally be used in any applicationrequiring energy storage. The devices may be particularly well suitedfor use in applications such as in electric vehicles, hybrid electricvehicles and grid storage and regulation.

Examples of Devices:

Devices may be made with the following dielectric and blocking layers

Dielectric Layer First Blocking Second Blocking Example Material LayerMaterial Layer Material 1 SiO₂ PZT PZT 2 SiO₂ LiPON LiPON 3 Li₂O LiPONLiPON 4 LiF LiPON LiPON 5 SiO₂ LiPON YSZ (yttria-stabilized zirconia,(Y₂O₃)_(x)(ZrO₂)_(1−x)

In one version of the energy storage devices described herein the highenergy density capacitive energy storage materials may have one or moreof the following characteristics:

-   -   1) Inhibit the onset of Fowler-Nordheim tunneling    -   2) Provide high breakdown strength    -   3) Are tolerant of defects arising during fabrication or during        high voltage stress

1) High Breakdown Strength

In one version, the devices described herein may have high breakdownstrength because a) FN tunneling is not dominant, (for example,calculations suggest that other failure mechanisms in SiO₂ limit thebreakdown tolerance to ˜20V/nm) b) the low-k material is intrinsically ahigh breakdown material (for example, because of high purity, low defectconcentration, high bandgap, etc.) c) the electric field is droppedprimarily in the low-k material, which has high breakdown strength d) byinterleaving thin nano-layers of the low-k material with the high-kmaterial, any free charge carriers in the conduction band may not gainsufficient kinetic energy to cause damage via impact ionization.

2) Defect Tolerance

To increase high voltage breakdown strength, it may be advantageous forthe material under voltage stress have a low defect concentration.Defects which introduce states in the middle of the band gap of theinsulator can lead to breakdown of the insulator. One mechanism by whichdefects lead to breakdown is that as defects form in a capacitor nearthe electrode, the field gets concentrated around those defects,enhancing the current around those defects, which leads to heating (andionization), which results in further defect creation, forming apositive feedback. In the laminate structure, this feedback betweendefects and current cannot occur, since the material adjacent to the(defective) insulator is not conducting.

FIG. 10 is a graph illustrating performance of an exemplary energystorage device with SiO₂ as dielectric material and PZT as blockingmaterial according to embodiments of the present invention. The graph isgenerated under the following conditions:

-   -   Matrix is modeled as “PZT”, ∈=400

PZT E _(dens)=0.5*400*∈₀*0.1 V/nm=4.9 Wh/l

-   -   blocking layer is modeled as SiO₂, ∈=3.9, which is 0.5 nm with        2.0 nm spacing

As illustrated in the graph of FIG. 10, through the thickness of theblocking material, a stable and substantially uniform electric field ismaintained at a about 0.48V/nm. When the applied electric field is about0.1 V/nm, and the energy density is about 0.23 Wh/l. The high ∈ regionhas low field, and low ∈ region has higher field. When the appliedelectric field is 2.2V/nm, the energy density is at about 112 Wh/l.

In an exemplary embodiment, the blocking layer is characterized by athickness of 2 nm with 2 nm spacing. When the applied energy is 0.1V/nm,the energy density is at about 0.095 Wh/l. When the applied energy is5.2V/nm, the energy density is at about 257 Wh/l.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

Numerous methods of fabrication of a device as described herein will beobvious to one skilled in the art. As a non-limiting example, onefabrication sequence is generically described below. A conductivesubstrate, or an insulting substrate with a conductive coating, forms afirst electrode. Alternating dielectric and blocking materials aredeposited by PVD, sputtering, evaporation, high rate evaporation, closespace sublimation, CVD, ALD, PECVD, or solution synthesis such as CBD,precipitation, spray coating, spin coating, roll coating, slot-die, etc.For example, SiO2 may be deposited by sputtering in an Applied MaterialsEndura 200 mm system by reactive RF sputtering of Si in an oxygenplasma. LiPON may be deposited in a similar fashion from a Li₃PO₄ targetin a nitrogen plasma. One or more stacks of dielectric/blocking layersmay be alternated in turn. A top electrode may be deposited by asolution process, or a vacuum process, for instance one selected fromthe list provided above. The device may be packaged for reliability andto prevent ingress of oxygen or humidity by any number of techniquescommon in semiconductor packaging, for example, by alternating layers ofparylene and titanium. The electrodes are fed through a hermetic seal ascommon in battery devices.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

1. An energy storage device comprising: first and second electrodesspaced apart; a dielectric layer comprising SiO₂ or SiO_(x)N_(y), anddisposed between the first and second electrodes; a first blocking layerdisposed between the first electrode and the dielectric layer; and asecond blocking layer disposed between the second electrode and thedielectric layer, wherein the dielectric constants of the first andsecond blocking layers are both independently greater than thedielectric constant of the dielectric layer, wherein the thicknesses ofthe first and second blocking layers are both independently less thanthe thickness of the dielectric layer, and wherein the first and secondblocking layers independently comprise a non-ionically conductingmaterial selected from PZT (Pb(Zr_(0.5)Ti_(0.5))O₃), SrTiO₃, PbTiO₃,BaTiO₃, (BaSr)TiO₃, CaCu₃Ti₄O₁₂, and La_(2-x)Sr_(x)NiO₄.
 2. The deviceof claim 1, wherein the thickness of the dielectric layer is between 1and 1000 times greater than the thicknesses of the first and secondblocking layers independently.
 3. The device of claim 1, wherein thethickness of the dielectric layer is between 1 and 1000 times greaterthan the thickness of the first blocking layer.
 4. The device of claim1, wherein the thickness of the dielectric layer is between 1 and 1000times greater than the thickness of the second blocking layer.
 5. Thedevice of claim 1, wherein the thicknesses of the first and secondblocking layers are independently between 4 nm and 100 nm.
 6. The deviceof claim 1, wherein the thickness of the dielectric layer is between 10nm and 10 um.
 7. The device of claim 1, wherein the thickness of thedielectric layer is between 20 nm and 10 um.
 8. The device of claim 1,wherein the device has an energy density of between 50 and 500 Whr/kg.9. The device of claim 1, wherein the device has an energy density ofgreater than 50 Whr/kg.
 10. The device of claim 1, wherein the devicehas an energy density of greater than 100 Whr/kg.
 11. The device ofclaim 1, wherein the first electrode has a work function greater thanthe work function of the second electrode.
 12. The device of claim 1,wherein the work function of the first electrode is greater than 4.0 eVand the work function of the second electrode is less than 4.5 eV.